Bilge pump switches which activate and deactivate a bilge pump motor depending on the presence or absence of liquid in the bilge hold of a marine vessel are well known for use in recreational boating. Historically, such switches have been made in the form of float operated switches involving moving parts which are subject to malfunction due to corrosion and the presence of contaminants in the liquid being sensed. Float switch systems possess additional disadvantages in that they are sensitive to orientation of mounting, and they are also inherently bulky.
Other bilge pump switches have been produced based on pressure switch systems typically comprising a sealed chamber covered by a movable membrane. As with float switches, such systems contain moving parts susceptible to mechanical malfunction and also include inherent disadvantages such as a proclivity toward pressure chamber leaks due to punctures in the membrane and sensitivity to temperature variations.
Due to the problems discussed above, it has become desirable to employ switching means controlled by non-mechanical devices which sense fluid levels using electronic detection means. To this end, some switching devices have been designed with probes which utilize the conductivity of the fluid being sensed in contact with the probes creating an electrical path to activate the bilge pump. However, these devices present their own problems with respect to corrosion of the probes and the more noteworthy problem of spark-induced combustion due to the potential presence of floating fuel in the bilge area.
The loss of property as well as lives from accidents which could be prevented serves as strong motivation for producing a safe and dependable switch control means for operating a bilge pump. Accordingly, the invention disclosed herein is directed toward the problems attendant with bilge pump systems by providing a non-mechanical switching means operating on the principles of acoustic wave propagation. The inventor notes that the present invention is not limited to bilge pumping systems but is also useful in other applications of pumping and/or liquid level sensing systems.